Silicone resin for protecting a light transmitting surface of an optoelectronic device

Abstract

A silicone resin composition and process for coating a light transmitting surface of an optoelectronic device is disclosed. The process involves applying a silicone resin to the light transmitting surface, and causing the silicone resin to cure to form a light transmitting protective coating on the light transmitting surface, the silicone resin having a sufficiently low proportion of organosiloxanes having molecular weights of up to about 1000, such that the protective coating includes less than about 10% of the organosiloxanes having molecular weights of up to about 1000.

1. An optoelectronic device comprising:
 a light transmitting surface of a light emitting diode (LED); and 
 a light transmitting protective coating of cured silicone resin on said light transmitting surface, said protective coating comprising less than about 10% of organosiloxanes having molecular weights of up to about 1000, wherein the silicone resin is formed by the process comprising:
 admixing a linear organopolysiloxane, an organohydrogenpolysiloxane, a substance having at least one of a phenyl and a cyclohexyl group to increase a refractive index of said cured silicone resin to at least about 1.45, and an adhesive aid for enhancing adhesion of said silicone resin to the light transmitting surface; and 
 removing at least a portion of the organosiloxanes having molecular weights below 1000 from said linear organopolysiloxane prior to admixing to reduce discoloration of the silicone resin for improved light transmission through the silicone resin. 
 
 
     
     
       2. The device of  claim 1  further comprising an overcoat layer on said protective coating, said overcoat layer being operable to seal said protective coating. 
     
     
       3. The device of  claim 1  wherein said protective coating comprises cured silicone resin having a Shore 00 hardness of up to about 85. 
     
     
       4. The device of  claim 1  wherein said substance having at least one of a phenyl and a cyclohexyl group in a proportion of at least about 10% by mole fraction. 
     
     
       5. The device of  claim 1  wherein said protective coating comprise at least one of:
 a phosphor material; 
 an inorganic filler material; and 
 an anti-oxidant operable to prevent discoloration of said protective coating. 
 
     
     
       6. The device of  claim 1  further comprising an optical element spaced apart from said light transmitting surface, and wherein said light protective coating is disposed between said light transmitting surface and said optical element. 
     
     
       7. The device of  claim 1  wherein said protective coating comprises less than about 8% of organosiloxanes having molecular weights of up to about 1000. 
     
     
       8. A process for coating a light transmitting surface of a light emitting diode (LED), the process comprising:
 providing the LED on a support structure such that electrical contacts on the LED are bonded to electrical contacts on the support structure; 
 providing components containing organosiloxanes, a substance having at least one of a phenyl and a cyclohexyl group to increase a refractive index of a resulting silicon resin to at least about 1.45, and an adhesive aid for admixing to form the-silicone resin, the adhesion aid for enhancing adhesion of said silicone resin to said light transmitting surface; 
 removing at least a portion of the organosiloxanes having molecular weights below 1000 from at least one of said components prior to admixing to reduce discoloration of the silicone resin for improved light transmission through the silicone resin; 
 admixing the components to form the silicone resin; 
 applying a silicone resin to the light transmitting surface after the electrical contacts on the LED are connected to electrical contacts on the support structure; and 
 causing said silicone resin to cure to form a light transmitting protective coating on the light transmitting surface, said silicone resin having a sufficiently low proportion of organosiloxanes having molecular weights of up to about 1000, such that said protective coating comprises less than about 10% of said organosiloxanes having molecular weights of up to about 1000. 
 
     
     
       9. The process of  claim 8  wherein admixing the components comprises admixing:
 a linear organopolysiloxane comprising at least one unsaturated aliphatic group participating in hydrosilylation reaction in a molecule; 
 an organohydrogenpolysiloxane; and 
 a platinum metal catalyst. 
 
     
     
       10. The process of  claim 9  wherein admixing said organohydrogenpolysiloxane comprises admixing an organohydrogenpolysiloxane in sufficient proportion to cause said silicone resin composition to cure to form a protective coating having a Shore 00 hardness of up to about 85. 
     
     
       11. The process of  claim 9  wherein admixing said linear organopolysiloxane comprises admixing a linear organopolysiloxane having a viscosity of about 0.3 to about 100 Pa-s at 23° C. 
     
     
       12. The process of  claim 9  wherein admixing said linear organopolysiloxane comprises admixing a linear organopolysiloxane having at least one of a phenyl and a cyclohexyl group. 
     
     
       13. The process of  claim 9  wherein said linear organopolysiloxane comprises an organopolysiloxane having the general formula: 
       
         
           
           
               
               
           
         
         wherein R 1  are each independently a substituted or unsubstituted monovalent hydrocarbon group, R 2  are each independently a substituted or unsubstituted monovalent hydrocarbon group excluding phenyl and cyclohexyl groups; each R 3  are each independently a phenyl or cyclohexyl group, each of L and m is 0 or a positive integer, with the proviso that at least one R 1  is a phenyl or a cyclohexyl group when m=0, and the sum of L+m is such a number that the organopolysiloxane has a viscosity of about 0.3 to about 100 Pa-s at 23° C. 
       
     
     
       14. The process of  claim 9  wherein removing at least a portion of the organosiloxanes comprises removing at least a portion of organosiloxanes having low molecular weights from said linear organopolysiloxane prior to said admixing. 
     
     
       15. The process of  claim 14  wherein said removing comprises at least one of alcohol washing and heating said linear organopolysiloxane. 
     
     
       16. The process of  claim 9  wherein admixing further comprises admixing at least one of:
 a phosphor material; 
 an inorganic filler material; 
 an anti-oxidant operable to prevent discoloration of said protective coating; and 
 a cure inhibitor operable to inhibit curing of the silicone resin after said admixing. 
 
     
     
       17. The process of  claim 8  further comprising overcoating said protective coating with a sealing material. 
     
     
       18. The process of  claim 8  wherein applying said silicone resin comprises applying a silicone resin having a sufficiently low proportion of organosiloxanes having molecular weights of up to about 1000, such that said protective coating comprises less than about 8% of said organosiloxanes having molecular weights of up to about 1000. 
     
     
       19. A silicone resin composition coating a light transmitting surface of an optoelectronic device, the composition comprising:
 a plurality of liquid components including:
 a linear organopolysiloxane component comprising at least one unsaturated aliphatic group participating in hydrosilylation reaction in a molecule; 
 an organohydrogenpolysiloxane component; 
 a platinum metal catalyst; 
 a substance having at least one of a phenyl and a cyclohexyl group to increase a refractive index of said silicone resin to at least about 1.45, and 
 an adhesive aid for enhancing adhesion of said silicone resin to the light transmitting surface, 
 
 wherein at least a portion of organosiloxanes having molecular weights below 1000 are removed from said linear organopolysiloxane component prior to admixing the components to reduce discoloration of the silicone resin for improved light transmission through the silicone resin, 
 said linear organopolysiloxane component having a sufficiently low proportion of organosiloxanes having molecular weights of up to about 1000, such that when said silicone resin product is cured said cured product comprises less than about 10% of said organosiloxanes having molecular weights of up to about 1000. 
 
     
     
       20. The silicone resin composition of  claim 19  wherein said liquid components are admixed with a cure inhibitor operable to inhibit curing of the silicone resin product prior to application on the light transmitting surface. 
     
     
       21. The silicone resin composition of  claim 19  wherein said liquid components are provided separately for combination into said silicone resin composition immediately prior to application on the light transmitting surface. 
     
     
       22. The silicone resin composition of  claim 19  further comprising at least one of:
 a phosphor material; 
 an inorganic filler material; and 
 an anti-oxidant operable to prevent discoloration of said cured product. 
 
     
     
       23. The silicone resin composition of  claim 19  wherein said linear organopolysiloxane component has a sufficiently low proportion of organosiloxanes having molecular weights of up to about 1000, such that when said silicone resin product is cured said cured product comprises less than about 8% of said organosiloxanes having molecular weights of up to about 1000.